We were excited when we spotted it as it was crossing our NACO field of view in seconds. We had to apply a fast tracking speed to the telescope (about 8.5 arcseconds per second of time). The adaptive optics loop struggled (I wish I had been there to press the buttons and try things. Gianluca did a good job I suppose but it's not the same, we really need a remote observing facility on Paranal.. hint hint). I then suggested to do some speckle imaging to attempt to reach the diffraction limit another way (than AO..) but the flux in Ks with 200 ms exposure was rather low. It's tough to hunt fast moving "rocks".

As they once pointed their webcam towards the real time display, I took a screen capture at the right time and 2005 YU55 is the white spot close to the center.

Here are two shot taken successively: the first one is a 20-s exposure and the second one is 95 minutes on the same field. While the morning light is coming up the starry one is spinning down. The colors of the brightest stars (among which the southern cross ones in the center of the field) are well preserved.